The present invention relates to molded parts for electronic devices, each obtained by inserting an insert article into a metallic mold and resin-molding the circumference of the insert article. More specifically, the invention relates to an integrally multiple-molded part for electronic devices, obtained by integrally insert-molding a plurality of electrical connection terminals a plurality of times. The invention is also directed to an electronic device that includes a circuit board with an electronic component mounted inside the integrally multiple-molded part for electronic devices.
The increase in electronic control of devices in recent years has brought about the proliferation of the molded parts each obtained by insert-molding from resin a plurality of terminals for electrical connection to outside. In these molded parts, from the viewpoints of productivity and reliability, wire bonding is most commonly used to bond the electrical connection terminals and a circuit board or the like having an electronic component mounted in the molded part.
The electrical connection terminals connected by wire bonding to the circuit board (or the like) having an electronic component mounted in such a molded part are resin-molded for mounting in a fixed condition inside the molded part itself.
When the electrical connection terminals are fixed, however, each of these terminals must be fixed to a desired position without deforming under a resin-filling pressure. Also, for the electrical connection terminals formed by insert-molding, from the viewpoints of their ease of handling and of their productivity, a multiple-molding method is most commonly used to obtain a molded part of the desired final shape or function. In this multiple-molding method, in order to link the plurality of electrical connection terminals, these terminals are first formed by primary molding from resin beforehand and then fixed using the primary molding resin. Next, these plural electrical connection terminals that have been fixed using the primary molding resin are further insert-molded as an insert, and integrated with secondary molding resin.
During the insertion of primary molding resin into the part to be formed by multiple molding, when the metallic mold is filled with fused resin, the fused resin shrinks in a solidification process and the primary molding resin undergoes a stress. The action of this stress causes the deforming stress that acts as bending force upon the product obtained by primary molding. The molding resin in contact in a clearance-free state with a bonding side face is pulled away therefrom by the deforming stress. Consequently, clearances occur and the so-called “rattling” results.
Aluminum wire bonding to the electrical connection terminals mentioned above is accomplished by overlapping an aluminum wire on the electrical connection terminals, then applying vibrational energy from the top of the aluminum wire by use of the bonding horn of a bonding machine, and utilizing the frictional force generated on the bonding surface of each electrical connection terminal and on the contact region of the aluminum wire. Accordingly, if the electrical connection terminals have a clearance or backlash during molding, when the aluminum wire is overlapped on the electrical connection terminals and then the bonding machine is operated to assign ultrasonic vibration via the bonding horn, the electrical connection terminals will become tuned to the aluminum wire and absorb the ultrasonic vibration. This may prevent sufficient frictional force from being generated on the bonding surface of each electrical connection terminal and on the contact region of the aluminum wire, with the result that the energy required for bonding may not be obtainable. If these actually happen, the problem will occur in that connection between the electrical connection terminals and the circuit board or the like having an electronic component mounted in the molded part cannot be established by wire bonding.
Related conventional methods for improving the adhesion between the primary molding resin and second-molding resin in a multiple-molded part are already disclosed. These methods, however, have been such that the metallic section molded by primary molding, such as a molded part for bonding, will have an exposed surface after secondary molding. Therefore, the suppression of the occurrence of the shrinkage stress acting between the metallic section and primary molding resin of the primary-molded article during secondary molding has been difficult. (See Japanese Patent Laid-open Nos. 2000-183468 and 9-300401).
For example, according to Japanese Patent Laid-open No. 2000-183468, during primary molding, the surface to be firmly bonded to the resin section during secondary molding is subjected to fine dimpling to improve adhesion. As described above, however, since the metallic section molded by primary molding, such as a molded part for bonding, will have an exposed surface after secondary molding, it will be difficult to suppress the occurrence of shrinkage stresses during secondary molding.
Also, according to Japanese Patent Laid-open No. 9-300401, a recessed portion and an edge portion are formed in the intermediate position of the linking section for linking the terminals formed as a primary-molded article, the edge portion is fused using the fusion heat of secondary molding resin, and thus the interface to the primary molding resin is removed to improve adhesion. As described above, however, since the metallic section molded by primary molding, such as a molded part for bonding, will have an exposed surface after secondary molding, it will be difficult to suppress the occurrence of a shrinkage stress during secondary molding.
Although this does not relate to a multiple-molded part, another method of preventing the occurrence of clearances between the electrical connection terminals and resin in a molded part for bonding is disclosed in Patent Reference 3, for example. In this method, terminal end portions other than the surface to be bonded have been coated with resin, or each terminal has been provided with bends and embedded in resin, or the reverse side of the section to be bonded has been grooved or dimpled.
According to Japanese Patent Laid-open No. 9-107059, as shown in FIG. 1 thereof, in a molded part that is formed by resin-insert-molding a plurality of terminals for electrical connection to outside, wire bonding is used frequently from the viewpoints of productivity and reliability to bond electrical connection terminals 2 and a circuit board (or the like) having an electronic component 92 mounted in the molded part. In this molded part for bonding, in order to prevent the occurrence of clearances between the electrical connection terminals 2 and resin in the part 1 formed by primary molding, terminal end portions other than the surface to be bonded are coated with resin, or each electrical connection terminal is provided with bends 2g, 2h and embedded in resin, or the reverse side of the terminal 2 is provided with a groove 2b or protrusions 2c, 2d.
Yet another conventional method of preventing the electrical connection terminals of such a bonding-use molded part from resonating with ultrasonic vibration has been executed by applying an adhesive such as an epoxy material to terminal end portions other than the surface to be bonded. That is to say, the applied epoxy resin is hardened for bonding, and movements of the electrical connection terminals are suppressed by utilizing the rigidity of the epoxy resin hardened integrally with the electrical connection terminals.
The increases in the compactness and multifunctionality of connection terminals in recent years, however, have made it necessary to arrange a greater number of connection terminals, and this tendency, in turn, is reducing the terminals in width and in arrangement pitch. Accordingly, the technique described in Patent Reference 3 is coming to pose at least two problems. One is that a sufficient bonding space cannot be obtained at the terminal end portions to be resin-coated or at the terminal end portions to be provided with bends. The other is that since the grooved or dimpled reverse side of the section to be bonded suffers significant plastic deformation, the surface to be bonded becomes prone to undulations, dents, or other defects, and deteriorates in quality. For the connection terminals that were reduced in terminal width, therefore, there has been a limit to the effectiveness of the technique descried in Patent Reference 3.
Also, to apply an epoxy material or any other suitable adhesive, the step of applying the epoxy material and the step of curing the applied epoxy material are required, and a curing time of about 30 to 60 minutes is required in the curing step. In addition, since such a manufacturing method requires an application machine and curing equipment, there has been a problem in that costs are increased by a decrease in productivity. Furthermore, the space required for the application of the epoxy material has been lost by the tendency towards reduced connection terminal areas due to the further compactness and multifunctionality of connection terminals in recent years, and the above method has also had its limits.